Microwave foods materials

The mote general food processing appHcations requite data on dielectric and thermal properties (139). Considerable effort has been expended by food companies in the design of food for the microwave oven. These principles have been reviewed (140). The microwave oven at 2450 MH2, used for reheating, cooking, and thawing foods, may also be used for drying (qv), eg, flowers or food materials (141). Commercial microwave ovens ate used extensively in restaurants and fast-food estabUshments. 

GE E-seminars (http //www. ge-plastics.com/resins/designsolutiony seminar/) GE s virtual conference center offers the ability to interact with GE Plastics real-time in live on-line conferences. E-Seminar examples include Material Selection, which provides the attendee with the knowledge, skills and competencies to determine how application requirements influence the material specification process and Materials for Single-Use Microwave Food Packaging, which reviews trends in the growing Freezer-to-Microwave Food Packaging industry. 

Gunasekaran, S. 1999. Pulsed microwave-vacuum drying of food materials. Dry. Technol. 17, 395-412. 

Multilayered materials can be readily formed using thermoforming including food packaging that may involve inclusion of layers of ethylene-vinyl alcohol copolymers, PS, polyolefins, and/or copolymers of vinylene dichloride and vinyl chloride. Microwavable food trays from (crystallized) PET are manufactured using thermoforming. 

The values of e and e" of a food material play a critical role in determining the interaction of the microwave electric field with the material. A discussion of these interactions follows. A "map" of foods plotted against their dielectric parameters was introduced by Bengtsson and Risman (1971). Table 1 gives values for the dielectric constant, loss factor and penetration depth, and Figure 1 shows a "map" of these values for common foods. 

Solid food materials have dielectric properties dependent upon their composition. In many instances, particularly when developing microwavable food products, it is necessary to know the effective bulk microwave properties of the product, crushed, as is, or when agglomerated together. Typical examples are peas, beans, com, pasta, flour... 

Bengtsson, N. and Risman, P. 1971. Dielectric properties of foods at 3 GHz as determined by a cavity perturbation technique. Measurement on food materials. Journal of Microwave Power. 6(2) 107-123. 

In summary, headspace concentration method is the usual way of analyzing the odor quality of packaging materials and has been shown to give reliable data which can be correlated with sensory evaluation data. Oven-heated microwavable packaging materials may pose a special flavor problem in the food consumed. 

Over 500 raw materials used to create flavors were analyzed through a series of experiments designed to characterize their heat absorption in the microwave oven. From the data gathered, we have proposed the Delta T (AT ) theory to describe the behavior of flavors in the microwave environment. The AT values calculated for these raw materials, which comprise a range of functional groups, allow for the extrapolation of our data to the thousands of rav materials currently used in creating food flavors. This ultimately will enable the design of flavors which are customized for microwave food applications. 

Castle, L., Jickels, S.M., Gilbert, J., Harrison, 1990, Migration testing of plastics and microwave-active materials for high-temperature food-use. Food Add. Contam. 7, 6, 779-796. 

A new generation of PLA materials that can withstand high temperatures and are suitable for microwavable food packaging. 

Table II gives the results of residual trypsin inhibitor levels for the various soymilk preparations. The 90 and 120 sec microwave treatments were the most effective in inactivating the trypsin inhibitor complex while hot water treated and unheated samples showed the highest levels. It is not surprising to find that microwave processing is more efficient than hot water in suppressing trypsin inhibitor considering the rapid penetration of food material by microwaves and the susceptibility of protein action to small heat induced changes in tertiary structure. Hence, Collins and McCarty (12) found microwaves produced a more rapid destruction of endogenous potato enzymes (polyphenol oxidase and peroxidase) than hot water heating.

Microwave-enhanced drying is used in the food, wood, textile and pharmaceutical industries. Microwaves (MW) enable selective heating of the moisture contained in microwave-transparent materials. The whole process proceeds at lower bulk temperatures and allows considerable energy savings. Also, the speed of the MW drying avoids unwanted degradation of some less stable components of the dried materials. 

Food materials are poor electric insulators and can store and dissipate energy when exposed to microwaves. Dielectric properties describe an interaction of an electromagnetic field with non- or low-conducting matter. The dielectric properties data are very limited in literature and usually available only for a few foods or food components. Wang et al. (2008), Tanaka et al. (2008), and Liao et al. (2001, 2002, 2003) have conducted experiments to get a better understanding of the dielectric properties of various food products. The dielectric properties of some food materials are shown in Table 3.1 (Regier and Schubert, 2001). 

The following are key examples of how microwave thermal processing could affect the physical and chemical properties of a food material being processed. Each example represents major research areas in food processing, for example, fruits and vegetables, dairy products, meat products, marine products, and essential oils. 

Venkatesh, M. S. and G. S. V. Raghavan. 2004. An overview of microwave processing and dielectric properties of agri-food materials. Biosystems Engineering 88 1-18. 

Fig. 9.2 Mechanisms of moisture transport inside unfrozen food materials during microwave heating. Adapted from Cui (2004).

Table 9.2 presents the SEC and drying efficiency values for different microwave-assisted drying processes of food materials, as determined by various research groups. The minimal theoretical value of SEC for a dryer is 2.3 MJ per kg of evaporated water, based on the maximal theoretical specific moisture extraction ratio (SMER) of 1.55 kg per kWh and the latent heat of water evaporation at 100 °C (Holtz et cd., 2009). These results are expected to depend heavily on the scale and design of dryers, as well as on the method used to measure energy consumption (Durance and Wang, 2002). 

Several groups have correlated the volume or size changes of food materials during microwave-assisted drying with the moisture content (Tab. 9.3). 

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